1. Field of the Invention
The present invention relates to a portable electronic device, generally known as an "IC card," which contains an integrated circuit (IC) chip having, for example, a non-volatile data memory and a control element such as a CPU.
2. Description of the related art including information disclosed under .sctn.1.97-1.99.
IC cards, for use as portable data-storing electronic devices, have been developed quite recently. Each IC card contains an IC chip which has a non-volatile data memory and a control element such as a CPU. The control element accesses the data memory in accordance with instruction data input thereinto from an external device, so that relevant data can be written into or read out from the data memory. The data memory itself is divided into a plurality of data areas, any one of which can be accessed, as required, by the control element.
In conventional IC cards, as can be understood from U.S. patent application Ser. No. 696,099 to Tamada et al., entitled "Portable Data Storing/Processing Device," some of the data areas of the data memory are, so to speak, "locked". These locked data areas cannot be accessed unless the personal identification numbers (PINs) which are assigned to them are first input. Examples of such PINs are the card manufacture's PIN, the card issuer's PIN, the card holder's PIN, and the like. Various items of instruction data are commonly available for the card manufacture, issuer, holder, etc. When a desired data area is locked which can be used by the card issuer only, the card issuer's PIN is input to the IC card, and then an instruction data item is input thereto, whereby the data stored in the desired data area is processed in accordance with the instruction data.
When, in the above circumstances, the instruction data is input to the IC card without the card issuer's PIN being input, the control element outputs, to an external device, response data indicating that the instruction designated by the instruction data cannot be executed, and accordingly does not process the data stored in the relevant data area. When invalid instruction data, i.e. data which cannot be processed in the IC card, is input to the IC card, the control element outputs response data indicating that such input instruction data has not been defined. Since, therefore, it is possible for anyone to determine what is valid and invalid instruction data, simply by inputting every possible instruction data item to the IC card and checking the response in each case, the conventional IC card cannot thus be considered as providing a sufficient degree of data security.